The long-term goal of this research is to understand how cell interactions with the glomerular basement membrane (GBM) contribute to glomerular development, filtration, and disease. Major components of basement membranes are laminins, heterotrimers of alpha, beta, and gamma chains. Laminins play important roles in kidney development and function. The laminin alpha5 chain is required for normal kidney development, having roles in both early metanephric induction and glomerular vascularization. Preliminary data show that 1) mice with altered levels of laminin alpha5 have chronic proteinuria and podocyte foot process effacement; 2) the Lutheran blood group glycoprotein (Lu), a novel receptor for alpha5, is expressed basally on podocytes, mesangial, and endothelial cells adjacent to the GBM; and 3) replacement of the G domain of laminin alpha5 with that of laminin alpha1 in transgenic mice results in ballooned glomerular capillaries. We propose to test three hypotheses: 1) In mice with altered levels of laminin alpha5, disruption of normal podocyte-matrix interactions leads to abnormal podocyte behavior, foot process effacement, and proteinuria; 2) Lu modulates podocyte-GBM interactions during development and in adults by cooperating with integrin and non-integrin receptors to interact with laminin alpha5 in the GBM; and 3) Mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the GBM. To investigate these hypotheses, we will: 1) Determine the cause of proteinuria in mice with altered expression of laminin alpha5. A combination of immunohistochemistry and electron microscopy will be used to characterize the composition of the aberrant GBM and podocyte responses to it. Additional insights will be gained from a newly generated conditional Lama5 knockout. 2) Analyze mice with a targeted mutation in the Lu gene. In addition, Lu mutants will be mated to integrin alpha3 and conditional dystroglycan mutants to investigate cooperative receptor interactions with the GBM. 3) Determine the mechanism whereby mesangial cells adhere to the G domain of laminin alpha5. The repertoire of receptors on mesangial cells will be determined, and adhesion assays will be used to investigate which can interact with laminin alpha5. Together, the results of these studies will lead to a more complete understanding of cell-matrix interactions in the kidney and could reveal new avenues for diagnosis and treatment of human kidney disease.